(a) Field of the Invention
The present invention relates to a liquid crystal display including an overcoat layer.
(b) Description of the Related Art
In a liquid crystal element, images are displayed by switching the orientation of liquid crystals between transparent conductive glass surfaces through an external electric field. The liquid crystals are aligned in a predetermined direction at the interface between the liquid crystals and the transparent conductive glass surface. The degree of uniformity in the liquid crystal alignment is an important factor for determining the display quality of the liquid crystal display.
Rubbing is a conventional method of aligning liquid crystals. In the rubbing method, a polymer layer (such as polyimide) is coated on a substrate (such as glass) and the surface is rubbed in a predetermined direction by using a fiber (such as nylon or polyester). A disadvantage of this method is that minute particles or an electrostatic discharge (ESD) may be generated when the fiber and the polymer layer are rubbed against each other, and they may cause a serious problem during the manufacturing of the liquid crystal panel.
To avoid this problem, an alternative alignment method that uses light is researched. In this photo-alignment method, anisotropy is provided to the polymer layer by light irradiation to align the liquid crystals.
The photo alignment method uses a polymer having an optical functional reactor such as azobenzene, cumarine, chalcone, and cinnamate, and an optical isomerization or a photo-crosslink may anisotropically take place by irradiating the polymers with the polarized light such that the polymer anisotropy is formed on the surface of the polymer layer, thereby aligning the liquid crystal in the predetermined direction.
In the conventional structure of the photo alignment layer, the vertical alignment layer is irradiated with ultraviolet (UV) rays at an oblique angle to determine the alignment direction and the alignment angle of the liquid crystals. If the photo alignment layer is used, the pixel is divided into multiple domains (four domains) by a simple method regardless of the size of the pixel to pre-tilt the liquid crystals. This pre-tilting that is achieved by photo alignment improves the transmittance and the response time of the liquid crystals when compared to the conventional patterned vertical array (PVA).
However, when a color filter or a black matrix (BM) is formed on the lower substrate, the pre-tilt angle of the alignment layer may be changed by external fluorescent lights having a UV wavelength in a specific region.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.